1. Field of the Invention
The present invention generally relates to a head drum apparatus employed in recording/reproduction apparatuses such as a video tape recorder (VTR) and a digital audio tape recorder (DAT). More particularly, the invention is concerned with a technique for reducing a friction between a magnetic tape and the head drum to thereby ensure a satisfactory contact between the tape and the drum.
2. Description of the Related Art
In recent years, a magnetic tape on which data or information can be recorded with a high density by using short wavelength signals has been developed and used in practical applications such as the VTR, DAT and others. When compared with the conventional tape, the tape intended for the applications mentioned above features an extremely thin magnetic layer and a very smooth surface, which are favorable for realizing a high noise-reduction capability. However, the tape is likely to adhere or stick to the drum surface because of the features mentioned above, as a result of which friction between the tape and the drum increases to such extent that adverse influence is exerted to the transportation of the tape. This phenomenon is remarkable when dew condensation takes place on the drum surface and therefore good contact of the head with the tape is required.
The head drum of an upper drum rotation type is now being replaced by an intermediate drum rotation type or an intermediate disk rotation type drum structure. However, in the case of the drum structure of the intermediate drum or disk rotation type, the area occupied by a fixed or stationary drum part increases, which results in an increase in the friction between the tape and the stationary drum part, unfavorable for the tape transportation. In particular, when dew condensation occurs on the drum surface, transportation of the tape tends to become more difficult.
As one of the methods for solving the problems mentioned above, it is conceivable to roughen the surface of the magnetic tape. In that case, however, another problem arises that the contact between the tape and the head is degraded. Under the circumstances, there is proposed in JP-A-54-72028 and JP-A-54-72029 a head drum structure in which a means for vibrating the magnetic tape is provided as a very small constituent part of the drum, as an attempt to solve the problems mentioned above, as shown in FIG. 14. Referring to FIG. 14, the head drum assembly 4 is comprised of stationary drum parts 22a and 22b and an intermediate disk 24 provided with a magnetic head 24h, and a dew condensation detecting device 3 is provided in a part of the outer peripheral surface of the drum 22b. A piezoelectric ceramic member is used to cause the tape to vibrate. As shown in FIG. 15, the ceramic member is disposed on a part of the outer peripheral surface of the stationary drum 22b in JP-A-54-72028 and has conductive layers formed of silver paste on the inner and outer surfaces thereof. Two metal layer are formed on the conductive layer of the tape contacting surface by metal plating. When dew condensation is detected by a dew detecting device 3, a high-frequency voltage is applied to the piezoelectric ceramic member, as a result of which the drum is caused to vibrate with a very small amplitude to thereby prevent the magnetic tape from sticking to the drum surface. According to the teachings disclosed in JP-A-54-72028, the piezoelectric ceramic member itself constitutes a part of the stationary drum. However, as a matter of practice, it is not easy to realize the mechanical precision requirement involved in forming the piezoelectric ceramic member so that the high-density recording can be ensured. Further, a method of manufacturing the head drum apparatus of the structure mentioned above will be much complicated and incur degradation in the yield.
In JP-A-54-72029 a piezoelectric ceramic member is employed of a bimorph structure which makes it possible to increase the amplitude of vibration.
In JP-A-56-114151, there is disclosed a drum structure in which an electric motor is employed as a high-frequency vibration generating device, as shown in FIG. 16 of the accompanying drawings. Referring to the figure, the head drum apparatus of the intermediate disk rotation type includes upper and lower drums 22a and 22b which are caused to vibrate in the rotational direction of the drums under vibration applied by a motor 5 via a connecting rod 6, whereby sticking of a magnetic tape to the drum surface is prevented. Parenthetically, a tape tension control is realized by making variable the position of a tape guide post with the aid of a mechanical spring. As the alternative, a method of controlling a reel motor in dependence on the position of the post as detected by using a Hall element may be adopted for the tape tension control. A problem of this known vibration generating mechanism is seen in that the vibration of a high frequency cannot be generated, whereby adverse influence is exerted to the quality of picture or audio signal as reproduced.
Furthermore, there are disclosed in JP-A-63291248, JP-A-63-291249 and JP-A-63-291250 techniques for transporting the magnetic tape under the effect of a traveling wave in the direction longitudinal or transversal of the tape transportation by applying a high-frequency voltage signal to a number of piezoelectric ceramic members provided groupwise. However, these known techniques also suffer a problem in respect to the tape tension control in that the position of the post varies due to change in the tension, as a result of which configuration of the tape transportation system is changed to affect adversely the tape running speed and hence the quality of picture as reproduced.